Fiber in the Diet Theory Doesn’t Help Digestion

In years to come, the past couple of decades of the twentieth century may well come to be known as ‘The Bran Age’; a time when it seemed that most of the diseases of Western civilization were being blamed on a lack of fibre in the diet, and we were all being exhorted to eat as much as possible to cure or prevent those diseases.

Diseases blamed on a lack of dietary fibre include: intestinal diseases such as cancer of the colon, appendicitis, constipation and irritable bowel syndrome as well as coronary heart disease, diabetes, obesity, deep vein thrombosis, varicose veins, hiatus hernia and gallstones.

What is fibre?

In a nutshell, fibre is that part of a vegetable which passes undigested through the human gastrointestinal tract. The major natural source of fibre is the cellulose that forms plant cell walls but there are a number of other kinds of fibre. The ones that scientists are interested in most are cellulose, hemicellulose, lignin and pectin.

Origins of the recommendations

The belief that regular bowel movement is important for health is very ancient. In 1932 a ‘New Health’ movement was promoted in which people were urged to include plenty of roughage in their diets and it was hoped then that the prompt passing of stools after each substantial meal would reduce the incidence of intestinal disease. (1)

Thirty years later Dr Dennis Burkitt, while working as a doctor in Africa, discovered that there was a much lower incidence of cancer of the colon among rural black Africans than among Europeans and Americans. He attributed this low incidence to their relatively crude diet. (2)

The theory was that fibre hastened the passage of the bowel contents thus allowing less time for cancer-inducing agents to form. This, of course, presupposed that food became carcinogenic in the gut and there was no evidence that it did. Neither was there any evidence that moving food through the intestine at a faster rate decreased the risk of cancer.

So the theory was unsubstantiated then by evidence and later it was to be disproved in practice when it was noticed that, when the rural Africans moved into towns and adopted a Western style low fibre diet, they continued to have a low incidence of colon cancer. A pattern which has also continued with the second generation. It should also be noted that the rural Africans’ lifestyle is quite different from that of the Western city dweller: their diet is different in that their energy intake is lower and they eat less protein, fat and sugar, but they are also not exposed to so many pollutants, toxins or mental stresses and any of these factors could be responsible for the difference in disease patterns.

Other studies have also shown that there are Western communities (the Mormons of Utah, for example) who also enjoy a low incidence of colon cancer but eat a low fibre diet. (3) Nevertheless, the later findings were not publicised, Burkitt’s theories caught the attention of the media who are always ready to exploit a good story. They expanded what was at best a very weak hypothesis into the treatment dogma of today which teaches that fibre is a panacea for all manner of illnesses. (4)

But it would be unfair to heap all the blame on the media. Commercial interests were quick to see the potential in the recommendation. Although Burkitt’s recommendations were based on vegetable fibre, bran has a far higher fibre content than vegetables and bran was a practically worthless by-product of the milling process which, until then, had been thrown away. Now, virtually overnight, it became a highly priced profit maker. Bran is quite inedible – there is no known enzyme in the human body that can digest it.

Nevertheless, backed by Burkitt’s fibre hypothesis, commercial interests could now promote it as a valuable food. The late John Yudkin, Professor Emeritus of Nutrition and Dietetics at London University, pointed out that ‘perhaps one reason for the wide acceptance of the suggestion that fibre is an important, if not essential, dietary component is that it had the enthusiastic support of commercial interests.’ He was writing in particular about the high-bran products, All Bran and Branslim. (5)

Dr Hugh Trowell, another strong advocate of dietary fibre, confirmed this in 1974, saying that ‘a serious confusion of thought is produced by referring to the dietary fibre hypothesis as the bran hypothesis, for many Africans do not consume cereal or bran but remain almost free of constipation, irritable bowel syndrome and diverticular disease’. (6)

Bran, very high in fibre, is the tough outer covering of cereal grains. Every civilisation in history has devised methods and implements solely for the purpose of separating bran from the grain so that they would not have to eat it, and even animals in the Third World today, which are fed bran in their food, reject it.

Fruit and vegetables contain quite small amounts of fibre (see Table) so that if a significantly larger amount is to be eaten, this will have a dramatic effect on the volume of food consumed. Thus the advice to increase fibre in the diet, if we are to use ‘natural’ sources, must involve a substantial change to the diet as a whole. And that is likely to be unpopular or we would be eating it already.

Food

g/100g

g/100kcal

Apples, raw

2.0

4.3

Beans, haricot, boiled

7.4

8.0

Cabbage, winter, boiled

2.8

18.7

Carrots, young, boiled

3.0

15.0

Potatoes, new, boiled

2.5

2.6

Plums, raw

2.9

8.0

Irritable bowel syndrome

The claims made for fibre are based on its rapid transit through the gut and, because of this property, bran has been a popular way to manage irritable bowel syndrome (IBS) for since the early 1970s. So, is it effective? The answer appears to be no.

A number of placebo controlled studies of bran in IBS have not shown any convincing effect of the fibre on overall symptom patterns. Results of a study from St Bartholomew’s Hospital in London, showed clearly that fifty-five percent were made worse compared to only ten percent made better. (7) All symptoms of IBS were exacerbated (made worse) by wheat bran, with bowel disturbance most often adversely affected, followed by distension and pain. The authors conclude: ‘The results of this study suggest that the use of bran in IBS should be reconsidered. The study also raises the possibility that excessive consumption of bran in the community may actually be creating patients with IBS by exacerbating mild, non-complaining cases.’

When several independent responses were analysed, the only significant improvements with bran treatment were in constipation; but then a number of people believe, wrongly, that they are constipated if they miss only a day. Some patients found that the added bran in their food induced or exacerbated (worsened) uncomfortable symptoms of flatulence, distension and abdominal pain. In these cases, reduction in the amount of bran eaten was recommended.

In addition, there is really no direct evidence that an increase of fibre by itself will prevent or cure any of the other diseases. As far as colon cancer is concerned, Burkitt’s theory was questioned with the suggestion that the low cancer rates in rural Africans may be due to their high early death rates from other causes so that they do not reach the age at which cancer peaks in Europeans. (8) As Europeans usually develop it in their seventies and the life-expectancy of Burkitt’s Africans was only around forty, why was it that this suggestion took so long to arrive at?

There is also a growing scepticism in the USA that lack of fibre causes cancer. And some studies have even suggested that a fibre-enhanced diet may increase the risk of colon cancer. (9) The idea that people must tolerate an unpalatable bran-rich diet to ward off such diseases is founded on extremely dubious hypotheses.

It had been shown in the mid-1980s that dietary fibre increased the risk of colon cancers. (10) In 1990 The British Nutrition Foundation admitted that the hypotheses that IBS, diverticulosis and colo-rectal cancer are caused by a deficiency of fibre had not been substantiated, neither have those that fibre might protect against diabetes, obesity and CHD. (11) The Seventh King’s Fund Forum on Cancer of The Colon and Rectum agreed: ‘The Forum commented that cereal fibre does not offer protection against cancer’. (12)

Dr M Inoue, et al published in 1995 an investigation of cancers at several colorectal subsites: ascending, transverse, descending, sigmoid, and rectum, within a Japanese hospital environment. They concluded that loose or soft faeces are a significant risk factor for cancer at these sites. (13) And bran loosens and softens faeces – that’s why it is recommended.

The following year Drs HS Wasan and RA Goodlad of the Imperial Cancer Research Fund showed that bran can increase the risk of colorectal cancers. (14)‘Many carbohydrates’, they say, ‘can stimulate epithelial*-cell proliferation* throughout the gastrointestinal tract.

*Epithelial is any animal tissue that covers a surface, or lines a cavity or the like, and that, in addition, performs any of various secretory, transporting, or regulatory functions.

*Proliferation the growth or production of cells by multiplication of parts; sometimes a rapid and often excessive spread or increase.

They conclude: ‘Until individual constituents of fibre have been shown to have, at the very least, a non-detrimental effect in prospective human trials, we urge that restraint should be shown in adding fibre supplements to foods, and that unsubstantiated health claims be restricted. . . . Specific dietary fibre supplements, embraced as nutriceuticals or functional foods, are an unknown and potentially damaging way to influence modern dietary habits of the general population.‘

This study spawned several critical letters. It comes as no surprise that half were from people connected with the breakfast cereal industry. (15)

The results of the largest, long-term trial to date, published in 1999, also suggest that, contrary to popular belief, high dietary fibre intake does not protect against colorectal cancer. (16) Researchers at Harvard Medical School and the Dana-Farber Cancer Institute, both in Boston, Massachusetts, studied 88,757 women over sixteen years. They say: ‘no significant association between fiber intake and the risk of (colorectal involving the colon and rectum) adenoma was found’. But there was what they call an ‘unexpected’ finding, in that, according to their data, a high consumption of vegetable-derived fiber was actually ‘associated with a significant increase (35%) in the risk of colorectal cancer’. They conclude ‘Our data do not support the existence of an important protective effect of dietary fiber against colorectal cancer or adenoma (non-malignant tumour)’.

It has been claimed that elevated fruit and vegetable consumption is associated with a reduced risk of breast cancer. To test this, twenty named researchers at seventeen cancer research centres in the USA, Germany, Netherlands, and Sweden examined the association between breast cancer and total and specific fruit and vegetable group intakes. Their studies included 7,377 incident invasive breast cancer cases occurring among 351,825 women. They found no association for green leafy vegetables, 8 botanical groups, and 17 specific fruits and vegetables and conclude: "These results suggest that fruit and vegetable consumption during adulthood is not significantly associated with reduced breast cancer risk". (17)

Clearly there are two sides to this debate and claims of benefit are by no means proven. That, of course, does not stop a variety of commercial interests from jumping on a very lucrative bran-wagon.

When the American Heart Association published its dietary recommendations in 1982, the US National Cancer Institute (NCI) and Kellogg’s got together to promote All Bran. (18) But by making such health claims, Kellogg’s effectively turned All Bran from a food into a drug – and drugs must be approved by the Food and Drugs Administration (FDA). This gave the FDA a problem as the NCI had already given its blessing to All-Bran. They have an even bigger problem now as these later studies, by and large, do not support the claims that fibre has a protective role in cancer.

Tests into the supposed benefits of increasing dietary intake of fibre soon showed that there could be other harmful side-effects:

Because it is indigestible, bran ferments in the gut and can induce or exacerbate flatulence, distension and abdominal pain. (19)

Although it is supposed to travel through the gut at a faster rate, it does not always do so and it has been shown to cause blockages. (20)

All the nutrients in food are absorbed through the gut wall and this takes time. It should be obvious, therefore, that if the food travels through faster, less will be absorbed. And, indeed, this is the case. Fibre is found to inhibit the absorption of zinc, (21) iron, calcium, phosphorus, magnesium, energy, proteins, fats and vitamins A, D, E and K. (22)

Phytate associated with cereal fibre (bran) also binds with calcium, iron, (23) and zinc, (24) causing malabsorption. For example, subjects absorbed more iron from white bread than from wholemeal bread even though their intakes of iron were fifty percent higher with the wholemeal bread. (25) Also, while white bread must have added calcium, the law does not require it of wholemeal bread.

Bran fibre has also been shown to cause faecal losses, (26) and negative balances of calcium, (27) iron, zinc, phosphorus, (28) nitrogen, fats, fatty acids and sterols thus depleting the body of these materials. (29)(A negative balance is where more is lost from the body than is absorbed, i.e. the body’s stores are depleted.)